This invention relates to hybrid semiconductor devices, and particularly to the automatic fabrication of semiconductor devices containing multiple, interconnected semiconductor chips.
While not limited thereto, the invention has particular utility in the fabrication of two phase (full wave) bridge rectifiers including four interconnected semiconductor rectifier chips and four terminals for connecting the bridge rectifiers into an electrical circuit. Such bridge rectifiers are used in large quantities, and highly automated processes have been developed for their manufacture.
In one process, for example, described in U.S. Pat. No. 5,484,097 to W. Heuvel, the subject matter of which is incorporated herein by reference, two semiconductor chips are mounted on two spaced apart support plates of each of two lead frames, and the two lead frames are disposed one on top of the other to provide two, two-chip stacks of chips. In one stack, the chips are stacked anode to anode, and in the other stack the chips are stacked cathode to cathode. The two lead frames, along with a third lead frame overlying the chip stacks, provide the necessary interconnections among the four chips as well as the device four terminals. The process described results in a single bridge rectifier. In practice, a plurality of devices, one each at a plurality of spaced apart device sites on the three-lead frame workpiece, are simultaneously (batch) fabricated.
The process is quite satisfactory except that a relatively large number (three) of separate lead frames are used; careful parts registrations are required and, in the process of mounting the individual chips on their respective support plates, one pair of chips for each bridge rectifier must be inverted with respect to the other pair thereof. All the chips are identical and, typically, are simultaneously identically fabricated as part of a single semiconductor wafer. In a final chip processing step, the wafer is diced into individual chips which, while completely separated, remain in a planar array of chips lightly adhered to, for example, a sheet of plastic. During mounting of the chips on the lead frames, two chips for each bridge rectifier are lifted from the array of chips and are directly transferred to and placed on a respective support plates of each lead frames. The other two chips for each bridge rectifier, however, must be removed from the array of chips and somehow turned upside down prior to their transfer to and placement on the other two lead frame support plates.
While many, and generally satisfactory techniques exist for the automatic inversion of semiconductor chips, the very fact that an extra process is required for one pair of chips not required for the other inevitably means that there is some loss of efficiency and some loss of product owing to parts breakage. The present invention eliminates the need for inverting one pair of chips relative to the other and, indeed, eliminates the practice of forming pairs of lead stacks. Also, preferably, only one chip mounting substrate is used.